Catalyst for purification of exhaust gas

Abstract

The present invention provides a wall flow type exhaust gas purification catalyst which is excellent in PM trapping performance and has a small initial pressure loss. An exhaust gas purification catalyst (1) includes a catalyst-coated filter (2) and inorganic powder particles (3). The catalyst-coated filter (2) includes a filter substrate (21) and a catalyst layer (22) provided on the pore walls of the filter substrate (21). The catalyst-coated filter (2) has a first end portion, a second end portion, a filter partition wall (21W), an inlet-side chamber, and an outlet-side chamber. The filter partition wall (21W) is porous. The inlet-side chamber is open at the first end portion and is closed at the second end portion. The outlet-side chamber is open at the second end portion and is closed at the first end portion. The inlet-side chamber and the outlet-side chamber are adjacent to each other with the filter partition wall (21W) interposed therebetween. The inorganic powder particles (3) are biased toward the surface of the filter partition wall (21W) that is adjacent to the inlet-side chamber in a cross section parallel to the thickness direction of the filter partition wall.

Description

TECHNICAL FIELD

[0001] The present application relates to a catalyst for exhaust gas purification. BACKGROUND

[0002] Exhaust gas discharged from an internal combustion engine contains harmful substances such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx). x In the purification of such exhaust gas, for example, a flow-through type catalyst for exhaust gas purification containing a platinum group metal as a catalyst metal is used.

[0003] In addition, exhaust gas discharged from a diesel engine contains particulate matter (PM) at a high concentration in addition to the above-described harmful substances. Therefore, in the purification of exhaust gas discharged from a diesel engine, a diesel particulate filter (DPF) is also used in order to remove PM from the exhaust gas.

[0004] In recent years, regulations on PM emission are strengthened, and not only exhaust gas discharged from a diesel engine but also exhaust gas discharged from a gasoline engine needs to remove PM. Therefore, a gasoline particulate filter (GPF) is gradually used in the purification of exhaust gas discharged from a gasoline engine.

[0005] As these particulate filters, for example, there is a wall-flow type catalyst for exhaust gas purification in which a catalyst is supported on a partition wall of a filter. If such a catalyst for exhaust gas purification is used, it is possible to reduce the installation space of an exhaust gas purification system and to lower the cost of the exhaust gas purification system.

[0006] The wall-flow type catalyst for exhaust gas purification is described, for example, in Patent Literature 1. In Patent Literature 1, it is described that a powder composed of, for example, a metal oxide is only stacked in the pores of a filter wall, i.e., a porous partition wall, of the wall-flow type catalyst for exhaust gas purification, and is filled to 50% of the total pore volume with the powder.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: International Publication No. 2019 / 197177 SUMMARY

[0010] An object of the present application is to provide a wall-flow type catalyst for exhaust gas purification which has excellent PM trapping performance and has a small initial pressure loss.

[0011] According to one embodiment of the present invention, there is provided an exhaust gas purification catalyst comprising: a catalyst-coated filter, wherein the catalyst-coated filter comprises a filter substrate and a catalyst layer provided on a pore wall of the filter substrate, has a first end portion, a second end portion, a filter partition wall, an inlet-side cell, and an outlet-side cell, the filter partition wall is porous, the inlet-side cell extends from the first end portion toward the second end portion, is open at the first end portion, and is closed at the second end portion, the outlet-side cell extends from the second end portion toward the first end portion, is open at the second end portion, and is closed at the first end portion, the inlet-side cell and the outlet-side cell are adjacent to each other with the filter partition wall interposed therebetween; and inorganic particles in powder form, which are present unevenly in a surface of the filter partition wall adjacent to the inlet-side cell in a cross section parallel to a thickness direction of the filter partition wall. Hereinafter, the above-described exhaust gas purification catalyst is also referred to as a "powder-attached catalyst-coated filter".

[0012] The term "inorganic particles in powder form" can be in a state in which the particles are not fixed to each other or to other articles, or can be in a state in which the particles are fixed to other articles by heat treatment or chemical treatment. The inorganic particles can be primary particles or secondary particles.

[0013] The inorganic particles unevenly present as described above can be confirmed by the following method. First, a cross section of a porous partition wall of the exhaust gas purification catalyst, i.e., a cross section of a portion of the exhaust gas purification catalyst corresponding to the filter partition wall, is imaged using a scanning electron microscope to obtain a gray scale image. The imaging is performed on a cross section of a portion of the porous partition wall having the same distance from the first end portion and the second end portion. Next, an analysis position obtained using an energy dispersive X-ray analysis device is specified in the previous gray scale image, and the intensity of characteristic X-rays from only the elements contained in the inorganic particles is measured. Here, line analysis along the thickness direction of the porous partition wall is performed. From the analysis result, the inorganic particles unevenly present as described above can be confirmed. Note that the inorganic particles unevenly present as described above can also be confirmed from a composite image in which points having luminance corresponding to the intensity of the characteristic X-rays and colored in the previous gray scale image are superimposed. Note that the first end portion and the second end portion are portions of the exhaust gas purification catalyst corresponding to the first end portion and the second end portion, respectively.

[0014] The inorganic particles unevenly present as described above can be configured to reduce pores having a large opening diameter.

[0015] The exhaust gas purification catalyst is a particulate filter including a catalyst layer. More specifically, the exhaust gas purification catalyst is a wall flow type exhaust gas purification catalyst in which exhaust gas passes through a first chamber corresponding to an inlet side chamber, pores of a porous partition wall, and a second chamber corresponding to an outlet side chamber in this order, and PM in the exhaust gas is trapped by the porous partition wall in the process.

[0016] Generally, the wall flow type exhaust gas purification catalyst is used to remove PM from exhaust gas discharged from an internal combustion engine such as a gasoline engine and a diesel engine. For example, the wall flow type exhaust gas purification catalyst is used in an automatically propelled vehicle including at least a portion of a gasoline engine or a diesel engine as a power source.

[0017] In the wall flow type exhaust gas purification catalyst, the catalyst layer is provided to promote combustion of PM trapped by the filter partition wall.

[0018] For example, in a gasoline automobile equipped with the wall flow type exhaust gas purification catalyst, which uses power generated in a gasoline engine as a propulsive force, the catalyst layer promotes combustion of trapped PM particularly during high-load operation in which the gasoline engine discharges exhaust gas at a high temperature, such as driving on a suburban road or an expressway.

[0019] In addition, exhaust gas discharged from a diesel engine is lower in temperature than exhaust gas discharged from a gasoline engine. Therefore, in a diesel automobile equipped with the wall flow type exhaust gas purification catalyst, which uses power generated in a diesel engine as a propulsive force, combustion of trapped PM is promoted by injecting fuel into the exhaust gas to raise the temperature of the exhaust gas. The catalyst layer promotes the combustion, and thus contributes to reduction of fuel injected into the exhaust gas.

[0020] In the above-described wall flow type exhaust gas purification catalyst, powder-like inorganic particles are disposed in the pores throughout the thickness of the filter partition wall. The inorganic particles reduce the effective pore diameter of the pores of the filter partition wall, and thus the PM trapping performance of such an exhaust gas purification catalyst is excellent. However, in the case of such an exhaust gas purification catalyst, the inorganic particles exist in the pores throughout the thickness of the filter partition wall, and thus the initial pressure loss is large.

[0021] In a cross section parallel to the thickness direction of the filter partition wall, when the powder-like inorganic particles are biased toward a surface of the filter partition wall that is adjacent to the inlet side chamber, the effective diameter of the pores in the above-described surface becomes small. Therefore, the PM trapping performance can be improved. In addition, in the case where the inorganic particles are biased toward the above-described surface of the filter partition wall in the cross section parallel to the thickness direction of the filter partition wall, inorganic particles hardly exist in portions other than the vicinity of the above-described surface of the filter partition wall. Therefore, the initial pressure loss of the exhaust gas purification catalyst having such a configuration is small.

[0022] In addition, in a cross section parallel to the thickness direction of the filter partition wall, the inorganic particles in powder form are biased to the aforementioned surface of the filter partition wall, and the exhaust gas purification catalyst can exert the effects described below.

[0023] As described above, the catalyst layer can promote the combustion of PM, but does not always sufficiently promote the combustion of PM generated in the catalyst layer. For example, in the case of a gasoline automobile equipped with a wall flow type exhaust gas purification catalyst, when repeatedly walking and stopping, short distance traveling, the amount of PM trapped exceeds the amount of PM combusted, and as a result, PM is accumulated in the wall flow type exhaust gas purification catalyst. In addition, in the case of a diesel automobile equipped with a wall flow type exhaust gas purification catalyst, PM is accumulated in the wall flow type exhaust gas purification catalyst during a period before fuel injection to exhaust gas is performed.

[0024] If PM is accumulated, the pressure loss generated in the wall flow type exhaust gas purification catalyst becomes large. If the pressure loss becomes large, the fuel consumption performance is reduced. Therefore, it is desirable that the increase in pressure loss accompanying the accumulation of PM be small.

[0025] In the case of a general wall flow type exhaust gas purification catalyst, for example, a wall flow type exhaust gas purification catalyst that does not include the aforementioned inorganic particles in powder form, at the initial stage of PM accumulation, PM is accumulated in the fine pores located in the surface region of the filter partition wall that is adjacent to the inlet side chamber, that is, in the fine pores whose distance from the face of the filter partition wall that is adjacent to the inlet side chamber is, for example, 30% or less of the thickness of the filter partition wall, and the amount of PM accumulation in these fine pores increases. If the amount of PM accumulation in these fine pores increases, the gas flow path in the filter partition wall becomes narrow or is occluded, and as a result, the pressure loss greatly increases. Therefore, at the initial stage of PM accumulation, as the amount of PM trapping increases, the pressure loss sharply increases.

[0026] If the accumulation of PM into the fine pores located in the aforementioned surface region proceeds to a certain extent, PM is accumulated on the face of the filter partition wall that is adjacent to the inlet side chamber. The accumulation layer composed of PM accumulated on this face is a granular layer having a low apparent density. In this granular layer, narrowing or occlusion of the gas flow path accompanying an increase in the amount of PM accumulation is difficult to occur. Therefore, during this period, the increase in pressure loss accompanying an increase in the amount of PM trapping is stabilized.

[0027] Thus, in a general wall flow type exhaust gas purification catalyst, at the initial stage of PM accumulation, the pressure loss sharply and greatly increases. Therefore, in the case of an automobile equipped with such an exhaust gas purification catalyst, the period during which the pressure loss is large accounts for a high proportion of the period from the start of PM accumulation to the combustion of PM and the sufficient reduction in the amount of accumulation thereof.

[0028] In a cross section parallel to the thickness direction of the filter partition wall, in the exhaust gas purification catalyst having the inorganic particles in powder form biased to the surface of the filter partition wall that is adjacent to the inlet side chamber, PM is less likely to reach the pores of the surface of the first chamber side that is away from the porous partition wall. Therefore, the amount of PM accumulated in the pores of the porous partition wall is small, and narrowing and clogging of the gas flow path in the porous partition wall are less likely to occur. Therefore, the exhaust gas purification catalyst has a small pressure loss due to the accumulation of PM.

[0029] In addition, in a cross section parallel to the thickness direction of the filter partition wall, when the inorganic particles in powder form are biased to the surface of the filter partition wall that is adjacent to the inlet side chamber, PM is easily trapped by the surface of the porous partition wall, and thus reduction in catalyst performance due to the accumulation of PM in the pores is less likely to occur.

[0030] According to another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the preceding aspects, wherein a majority of the inorganic particles are located in the pores of the filter partition wall. When a majority of the inorganic particles are located in the pores of the filter partition wall, high PM trapping performance is easily achieved because PM is less likely to pass through the porous partition wall of the exhaust gas purification catalyst. In terms of a majority of the inorganic particles being located in the pores of the filter partition wall, preferably, the amount of the inorganic particles located in the pores of the filter partition wall accounts for 70% or more of the total amount of the inorganic particles.

[0031] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the preceding aspects, wherein a ratio D1 / D2 of an average particle diameter D1 of the inorganic particles to an average pore diameter D2 of the pores of the filter partition wall is in the range of 0.06 to 2. In the case where the ratio D1 / D2 is small, high PM trapping performance is less likely to be achieved. In addition, in the case where the ratio D1 / D2 is small, accumulation of PM in the pores is easily generated, and thus the pressure loss due to the accumulation of PM in the porous partition wall tends to be large. In the case where the ratio D1 / D2 is large, the initial pressure loss of the exhaust gas purification catalyst is easily large. In terms of the ratio D1 / D2, according to one example, the ratio D1 / D2 is in the range of 0.06 to 1. In terms of the ratio D1 / D2, according to another example, the ratio D1 / D2 is in the range of 0.15 to 2. The ratio D1 / D2 is preferably in the range of 0.15 to 0.7.

[0032] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the preceding aspects, wherein the filter substrate includes a honeycomb structure and a plug.

[0033] The honeycomb structure is a columnar body having a pair of opposite bottom surfaces, and is provided with a plurality of through-holes extending from one bottom surface to the other. One of the bottom surfaces corresponds to the first end, and the other bottom surface corresponds to the second end. The shape of the pair of opposite bottom surfaces is, for example, circular, elliptical, oblong, or polygonal.

[0034] The honeycomb structure includes partition walls constituting the side walls of the through-holes. The partition walls are porous, and separate adjacent through-holes.

[0035] As the material of the honeycomb structure, for example, ceramics such as cordierite, aluminum titanate, and silicon carbide can be used. In such a honeycomb structure, a nonwoven fabric made of metal or alloy can be incorporated. Alternatively, as the material of the honeycomb structure, metal or alloy such as stainless steel can be used.

[0036] Each plug closes the through-hole of the honeycomb structure at the one end side. Half of the plurality of through-holes are closed at the second end side by the plugs. The first chamber is a space surrounded by the plug closing the through-hole at the second end side and the partition wall constituting the side wall of the through-hole.

[0037] The remaining through-holes of the honeycomb structure that are not closed at the second end side are closed at the first end side by the plugs. The second chamber is a space surrounded by the plug closing the through-hole at the first end side and the partition wall constituting the side wall of the through-hole.

[0038] The first chamber and the second chamber are adjacent to the partition wall of the filter substrate and the catalyst layer formed in the fine pores of the partition wall.

[0039] As the material of the plug, for example, ceramics such as cordierite, aluminum titanate, and silicon carbide can be used.

[0040] According to still another aspect of the present application, there is provided the exhaust gas purifying catalyst according to any one of the above aspects, wherein the volume V of the filter substrate is in the range of 0.1 to 5 L. Here, the "volume" of the filter substrate is the volume including the spaces of the filter substrate corresponding to the first and second chambers and the partition wall, and is calculated by multiplying the area of the bottom surface of the filter substrate by the height of the filter substrate. The volume V of the filter substrate is preferably 0.5 L or more. In addition, the volume V of the filter substrate is preferably 3 L or less, and more preferably 2 L or less.

[0041] According to still another aspect of the present application, there is provided the exhaust gas purifying catalyst according to any one of the above aspects, wherein the size in the length direction of the entry-side chamber and the exit-side chamber of the filter substrate is in the range of 10 to 500 mm. The size is preferably in the range of 50 to 300 mm.

[0042] According to another aspect of the invention, a catalyst for exhaust gas purification is provided in any of the above-described embodiments, wherein the thickness of the portion of the filter substrate corresponding to the filter partition, i.e., the partition of the filter substrate, is in the range of 0.05 to 2 mm. If this thickness decreases, the mechanical strength of the filter substrate decreases. If this thickness increases, the porous partition becomes thicker, resulting in an increase in pressure loss (i.e., initial pressure loss) in the state where PM has not accumulated. This thickness is preferably in the range of 0.1 to 1 mm.

[0043] According to another aspect of the present invention, a catalyst for exhaust gas purification is provided in any of the above-described embodiments, wherein the porosity of the portion of the filter substrate corresponding to the filter partition, i.e., the partition of the filter substrate, is in the range of 30% to 90%. Note that this "porosity" is a value obtained using the mercury infiltration method. If the porosity increases, the mechanical strength of the filter substrate decreases. If the porosity decreases, the porosity of the porous partition also decreases, resulting in increased pressure loss in the absence of PM accumulation. Preferably, the porosity is in the range of 40% to 80%.

[0044] According to another aspect of the present invention, a catalyst for exhaust gas purification is provided in any of the above-described embodiments, wherein the average pore size of the portion of the filter substrate corresponding to the filter partition, i.e., the partition of the filter substrate, is in the range of 5 to 50 μm. It should be noted that this "average pore size" is a value obtained using the mercury infiltration method. If the average pore size increases, the mechanical strength of the filter substrate decreases. If the average pore size decreases, the pressure loss increases in the absence of PM accumulation. The average pore size is preferably in the range of 10 to 40 μm.

[0045] According to another aspect of the present invention, a catalyst for exhaust gas purification according to any of the above-described embodiments is provided, wherein the catalyst layer contains a noble metal. The noble metal is an example of a catalyst metal. For example, a platinum group element. The catalyst layer may contain one or more of, for example, platinum, palladium, and rhodium as a noble metal. These noble metals have a high ability to promote the combustion of PM.

[0046] According to another aspect of the present invention, a catalyst for purifying waste gas is provided, wherein the mass M of the precious metal is... M The ratio M to the volume V of the filter substrate M / V is in the range of 0.01 to 10 g / L. Compared to M M When / V is small, the effect of precious metals on promoting PM combustion is small. If it is smaller than M... M As / V increases, it becomes a high-cost process. Compared to M... M / V is preferably in the range of 0.1 to 5 g / L.

[0047] According to another aspect of the present invention, a catalyst for purifying exhaust gas is provided in any of the above-described embodiments, wherein the catalyst layer further comprises at least one of a porous support loaded with the noble metal and a co-catalyst. If a porous support is used, the specific surface area of ​​the noble metal is easily increased. If a co-catalyst such as an oxygen storage material is used, for example, the performance changes of the catalyst associated with variations in the composition of the exhaust gas can be reduced.

[0048] The porous support and cocatalyst are, for example, alumina; a composite oxide of cerium dioxide and zirconium oxide; a composite oxide as the main component, and also containing one or more polycrystalline or single-crystal oxides selected from rare earth elements other than cerium, oxides of alkaline earth metal elements, oxides of transition metal elements other than zirconium, alumina, and silicon dioxide; or a combination of two or more of them.

[0049] The average particle size of the porous support and the co-catalyst is preferably in the range of 0.05 to 5 μm, more preferably in the range of 0.1 to 3 μm. It should be noted that this "average particle size" is the median particle size obtained by laser diffraction and scattering.

[0050] According to another aspect of the present invention, a catalyst for purifying exhaust gas is provided, wherein the mass M of the catalyst layer is... C The ratio M to the volume V of the filter substrate C / V is below 300g / L. Compared to M C / V is preferably 250g / L or less, more preferably 150g / L or less, even more preferably 120g / L or less, and even more preferably 100g / L or less.

[0051] According to another aspect of the present invention, a catalyst for purifying exhaust gas is provided, wherein the mass M of the catalyst layer is... C The ratio M to the volume V of the filter substrate C / V is in the range of 10 to 300 g / L. Compared to M C When / V is small, the catalyst layer contributes little to reducing the size of large pores. If it is smaller than M... C As / V increases, the pressure loss increases when PM does not accumulate. (Compared to M) C / V is preferably in the range of 20 to 250 g / L, more preferably in the range of 20 to 200 g / L, and even more preferably in the range of 30 to 100 g / L. Compared to M C The lower limit of / V can be 25g / L. Additionally, compared to M... C The upper limit of / V can be 150g / L.

[0052] According to another aspect of the invention, a catalyst for exhaust gas purification is provided in any of the above-described embodiments, wherein at least a portion of the catalyst layer is located in the portion of the filter partition adjacent to the inlet chamber, i.e., the portion of the filter partition on the inlet chamber side. Herein, "the portion of the filter partition adjacent to the inlet chamber" refers to the portion of the filter partition where the distance between the surface of the portion adjacent to the inlet chamber and the surface of the filter partition is less than 80% of the thickness of the filter partition. The catalyst layer may also be entirely located in the portion of the filter partition adjacent to the inlet chamber, i.e., the portion of the filter partition on the inlet chamber side. Alternatively, the catalyst layer may be provided throughout the entire thickness of the filter partition. That is, the catalyst layer preferably extends from the inlet chamber side surface of the filter substrate partition to the vicinity of the outlet chamber side surface of the partition, for example, from the inlet chamber side surface of the filter substrate partition to the outlet chamber side surface of the partition. Such a configuration is particularly advantageous in reducing pressure loss in the absence of PM accumulation. In addition, this structure is particularly advantageous in enabling PM to burn reliably and in purifying other harmful substances.

[0053] According to another aspect of the present invention, a catalyst for exhaust gas purification is provided in any of the above-described aspects, wherein, in a cross-section perpendicular to the surface, the portion of the filter partition adjacent to the inlet chamber, i.e., the portion of the filter partition on the inlet chamber side, divides the fine pores inside the filter substrate into first fine pores with a pore diameter of 5 μm or more and less than 10 μm, second fine pores with a pore diameter of 10 μm or more and less than 20 μm, and third fine pores with a pore diameter of 20 μm or more, and the catalyst layer of the first fine pores generates a filling rate R. F1 The fill rate R generated by the catalyst layer in the second fine pore F2 The fill rate R generated by the catalyst layer of the third pore F3 Satisfying the inequality: R F1 <R F2 <R F3 The relationship shown.

[0054] Among them, the fill rate R F1 S is the total area S of the portion of the catalyst layer located within the first pore in the cross-section. C1 The total area S of the first fine hole F1 The ratio. Fill rate R F2 S is the total area S of the portion of the catalyst layer located within the second pore in the cross-section. C2 The total area S of the second fine hole F2 The ratio. Fill rate R F3 S is the total area S of the portion of the catalyst layer located within the third pore in the cross-section. C3 The total area S of the third fine holeF3 the ratio of the volume of the third pores to the volume of the second pores.

[0055] wherein the boundary between the continuous pores and the pore diameter of each pore are determined by the method described later with reference to the drawings.

[0056] The constitution determined using the above inequality can be utilized to suppress an increase in pressure loss in a state where PM does not accumulate and to achieve high PM trapping performance.

[0057] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein the packing rate R F1 is 40% or less, the packing rate R F2 is 40% or less, and the packing rate R F3 is 45% or less.

[0058] If these packing rates increase, the pressure loss in a state where PM does not accumulate increases.

[0059] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein the packing rate R F3 is 20% or more. In the case where the packing rate R F3 is small, it is not possible to arrange a sufficient amount of catalyst in the flow path of the exhaust gas, which is disadvantageous for the purification of harmful substances.

[0060] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein the packing rate R F1 is 10% or more, and the packing rate R F2 is 15% or more.

[0061] The packing rate R F1 and the packing rate R F2 are preferably small. Since a large portion of the exhaust gas flows through the third pores, it is preferable to reduce the packing rate R F1 and the packing rate R F2 and increase the packing rate R F3 from the viewpoint of the combustion of PM and the purification of other harmful substances.

[0062] According to a further aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein the total amount A of the inorganic particles, the amount Al of the inorganic particles on the surface of the catalyst-coated filter adjacent to the inlet-side chamber, i.e., the surface of the inlet-side chamber side of the catalyst-coated filter, and the amount A2 of the inorganic particles within the pores of the catalyst-coated filter at a distance of 20% or less of the thickness of the filter partition wall of the catalyst-coated filter from the surface of the catalyst-coated filter adjacent to the inlet-side chamber, i.e., the portion of the catalyst-coated filter corresponding to the filter partition wall, satisfy the relationship represented by the inequality (Al + A2) / A ≥ 90%.

[0063] The proportion (Al + A2) / A, which represents the degree to which the inorganic particles are biased toward the first chamber side of the porous partition wall, is preferably 90% or more. There is no upper limit to the proportion (Al + A2) / A. The proportion (Al + A2) / A can be 100%.

[0064] According to a further aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein the inorganic particles have an average particle diameter in the range of 1 to 50 μm.

[0065] The "average particle diameter" is the median particle diameter obtained using the laser diffraction / scattering method. Inorganic particles having an average particle diameter in the above range are likely to achieve, for example, high PM trapping performance. The average particle diameter is preferably in the range of 5 to 10 μm.

[0066] According to a further aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein the inorganic particles contain one or more selected from the group consisting of metal oxides, metal hydroxides, metal carbonates, metal phosphates, metal nitrates, metal sulfates, clay minerals, and porous inorganic substances.

[0067] Preferably, the inorganic particles are composed of one or more selected from the group consisting of metal oxides, metal hydroxides, metal carbonates, metal phosphates, metal nitrates, metal sulfates, and porous inorganic substances.

[0068] The metal element contained in the inorganic particles is, for example, one or more selected from the group consisting of alkali metal elements, alkaline earth metal elements, rare earth elements, and transition metal elements. The metal element is preferably one or more selected from the group consisting of calcium, magnesium, strontium, barium, aluminum, silicon, titanium, zirconium, and cerium.

[0069] Specific examples of inorganic particles include, for example, metal oxides such as calcium oxide, cerium oxide, titanium dioxide, zirconium dioxide, silicon dioxide, aluminum oxide, mixtures thereof, and mixed oxides. The clay minerals can be synthetic or natural. As porous inorganic materials, one or more types of zeolite and sepiolite can be used, for example. The inorganic particles preferably contain calcium oxide, and more preferably consist of calcium oxide.

[0070] According to another aspect of the present invention, a catalyst for exhaust gas purification is provided in any of the above-described embodiments, wherein, in a powder-added catalyst-coated filter, the mass M of the inorganic particles is... P The ratio M relative to the volume V of the filter substrate P / V is above 3g / L.

[0071] If compared to M P If / V is small, it is difficult to achieve high PM capture performance. Compared to M... P / V is preferably above 5g / L.

[0072] According to another aspect of the present invention, a catalyst for purifying exhaust gas is provided in any of the above-described embodiments, wherein the mass M of the inorganic particles is... P The ratio M relative to the volume V of the filter substrate P / V is below 50g / L.

[0073] If the ratio M is increased P / V, then the pressure loss increases when PM does not accumulate. Compared to M P / V is preferably 15g / L or less, more preferably 10g / L or less.

[0074] According to another aspect of the present invention, a catalyst for purifying exhaust gas is provided in any of the above-described embodiments, wherein the mass M of the inorganic particles is... P The ratio M relative to the volume V of the filter substrate P / V is in the range of 3 to 15 g / L. Compared to M P / V is preferably in the range of 5 to 10 g / L.

[0075] According to another aspect of the present invention, a catalyst for exhaust gas purification is provided in any of the above-described aspects, wherein, with regard to the portion of the catalyst for exhaust gas purification corresponding to the filter partition, i.e., the porous partition, the total area S of pores with an opening diameter of less than 40 μm on the surface is... S The proportion of the total area S of all the pores S S / S is above 65%. If the proportion S S When the pressure ratio is above 65%, the pressure loss due to PM accumulation is small.

[0076] wherein the "opening diameter" is a value obtained by the following method.

[0077] First, the surface of the first chamber side of the porous partition wall of the exhaust gas purification catalyst was photographed at a magnification of 200 times, and a gray scale image was obtained. For this photographing, an optical microscope was used. In addition, the photographing was performed on a region near the center in the length direction of the catalyst-coated filter in the surface of the first chamber side of the porous partition wall. Note that this "length direction" is the same as the length direction of the first and second chambers. Next, the obtained gray scale image was binarized, and a binarized image was obtained. Then, the area of each of the black portions of the first chamber side surface in the binarized image was found, and the diameter of a circle having an area equal to the area (i.e., the circle equivalent diameter) was set as the "opening diameter" of the fine pore corresponding to the black portion. Note that as long as a certain black portion is separated from other black portions, it corresponds to one fine pore regardless of its shape. Note that in this image processing, the image processing software "ImageJ" can be used.

[0078] the proportion S S The proportion S S The proportion S S The proportion S

[0079] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein, with respect to the portion of the exhaust gas purification catalyst corresponding to the filter partition wall, i.e., the porous partition wall, the total area S M The proportion S M The proportion S

[0080] If the proportion S S The proportion S M The proportion S M The proportion S S The proportion S M The proportion S

[0081] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein, with respect to the portion of the exhaust gas purification catalyst corresponding to the filter partition wall, i.e., the porous partition wall, the total area S L The proportion S L The proportion S

[0082] If the ratio S S / S increases, the ratio S L / S tends to decrease. The ratio S L / S is preferably 10% or less. For the ratio S L / S, there is no lower limit value, and according to an example, the ratio S L / S is 1% or more.

[0083] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein, for a portion of the exhaust gas purification catalyst corresponding to the filter partition wall, i.e., the porous partition wall, the total area S SS of the fine pores having an opening diameter of 20 μm or less on the surface is 50% or less of the total area S SS of all the fine pores.

[0084] The ratio S SS / S of the exhaust gas purification catalyst is larger than the ratio S SS / S of the exhaust gas purification catalyst, the pressure loss in the state where PM is not accumulated tends to be large. For the ratio S SS / S, there is no lower limit value, and according to an example, the ratio S SS / S is 20% or more.

[0085] According to still another aspect of the present application, there is provided the exhaust gas purification catalyst according to any one of the above aspects, wherein, in the catalyst-coated filter, the fine pores of the portion of the exhaust gas purification catalyst corresponding to the filter partition wall, i.e., the porous partition wall, are divided into first small fine pores having an opening diameter of 40 μm or less and first large fine pores having an opening diameter of 40 μm or more, and in the surface of the portion of the catalyst-coated filter corresponding to the filter partition wall, i.e., the filter partition wall, on the first chamber side, the fine pores possessed by the filter partition wall are divided into second small fine pores having an opening diameter of 40 μm or less and second large fine pores having an opening diameter of 40 μm or more, and the total area S S2 of the second small fine pores is 40% or less of the difference S S1 between the total area S S2 -S S1 of the first small fine pores. S2 of the second small fine pores, and the ratio (S S2 -S S1 ) / S S2 is 40% or less, and the total area S L2 of the second large fine pores is 40% or less of the difference S L1 between the total area S L2 of the first large fine pores. L1the total area S of the second large pores L2 the ratio (S L2 -S L1 ) / S L2 is 60% or more.

[0086] In the case where the ratio (S L2 -S L1 ) / S L2 and the ratio (S S2 -S S1 ) / S S2 Satisfying the above-mentioned requirements, the inorganic particles cause a greater degree of reduction in the opening diameter than in the case of the small pores. Such a configuration is, for example, advantageous in terms of obtaining a structure in which the ratio S S / S is large and the ratio S SS / S is small.

[0087] According to still another aspect of the present application, there is provided a method for manufacturing the exhaust gas purification catalyst according to any one of the above-mentioned aspects, including: forming the catalyst layer provided on the pore walls of the filter substrate; and supplying the inorganic particles to the surface.

[0088] The catalyst layer can be formed, for example, by the following method.

[0089] First, a slurry containing a raw material of the catalyst layer and a dispersion medium is prepared.

[0090] The raw material of the catalyst layer contains at least one of a catalyst metal and, optionally, a porous support and a promoter. The catalyst metal can be contained in the slurry, for example, in the form of a metal compound that can be dissolved in the dispersion medium, or in the form of a supported catalyst in which the catalyst metal is supported on a porous support. The dispersion medium is, for example, an aqueous solvent such as water.

[0091] The slurry is prepared in such a manner that it has an appropriate viscosity. For example, the slurry is prepared in such a manner that the viscosity at a shear rate of 400 s -1 is greater than 50 mPa-s and 150 mPa-s or less, and preferably in such a manner that it becomes 60 to 110 mPa-s or less.

[0092] wherein the viscosity of the above-mentioned slurry is a viscosity that can be measured at ordinary temperature using a commercially available shear viscometer. For example, the viscosity at the shear rate as described above can be easily measured by using a dynamic viscoelasticity measuring device (rheometer) that is standard in the field. Here, "ordinary temperature" refers to a temperature within a temperature range of 15 to 35°C, typically a temperature within a temperature range of 20 to 30°C, for example, 25°C.

[0093] The slurry can further contain a viscosity increasing agent. As the viscosity increasing agent, for example, a cellulose-based polymer such as carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), and hydroxyethyl methyl cellulose (HEMC) can be used. The proportion of the viscosity increasing agent in the total solid content of the slurry is not particularly limited as long as the viscosity of the slurry satisfies the above range, and is preferably in the range of 0.1 to 5% by mass, more preferably in the range of 0.3 to 4% by mass, and further preferably in the range of 0.5 to 3% by mass.

[0094] Next, the above slurry is supplied from the portion of the filter substrate corresponding to the first end portion, that is, the first end side of the filter substrate, and the gas in the filter substrate is sucked from the portion of the filter substrate corresponding to the second end portion, that is, the second end side of the filter substrate. Thereby, the slurry flows into the chambers opened at the first end portion of the filter substrate, and the slurry flows from the surfaces of the partition walls into the pores of the partition walls.

[0095] Next, the above slurry is supplied from the portion of the filter substrate corresponding to the second end portion, that is, the second end side of the filter substrate, and the gas in the filter substrate is sucked from the portion of the filter substrate corresponding to the first end portion, that is, the first end side of the filter substrate. Thereby, the slurry flows into the chambers opened at the portion of the filter substrate corresponding to the second end portion, and the slurry flows from the surfaces of the partition walls into the pores of the partition walls. Note that this process can be omitted.

[0096] The conditions of the above suction can vary depending on the cross-sectional diameter of the filter substrate, etc. In the case of a cylindrical filter substrate having a diameter in the range of 80 to 250 mm, for example, the suction is preferably performed under conditions in which the linear velocity (air velocity) of the gas flow near the end portion of the filter substrate when the filter substrate is disposed in the device without the supply of the slurry becomes in the range of 10 to 80 m / s. The suction time is not particularly limited, and is preferably in the range of 0.1 to 30 seconds. The preferable combination of the linear velocity and the suction time is 20 to 70 m / s and 0.5 to 25 seconds; and 40 to 60 m / s and 2 to 15 seconds.

[0097] Then, the filter substrate to which the slurry is supplied is dried, and is subjected to firing. As described above, a catalyst-coated filter is obtained. If a slurry having a high viscosity is used, and the suction is performed under the above conditions, a catalyst-coated filter having a higher R F1 , R F2 , and R F3 satisfying the above conditions.

[0098] Next, the inorganic particles are supplied to the catalyst-coated filter. Specifically, an aerosol containing the inorganic particles as aerosol particles is supplied to the first end portion of the catalyst-coated filter. At the same time, the gas in the catalyst-coated filter is sucked from the second end portion of the catalyst-coated filter. The suction is preferably performed in a manner that the first end portion of the catalyst-coated filter faces downward.

[0099] By this operation, the aerosol flows into the chamber opened at the first end portion side of the catalyst-coated filter, and is separated into the gas and the inorganic particles by the filter partition wall of the catalyst-coated filter. The gas flow path composed of the fine pores having a large pore diameter has a small air passage resistance as compared with the gas flow path composed of the fine pores having a small pore diameter. Therefore, the inorganic particles are more accumulated in the fine pores having a large pore diameter as compared with the fine pores having a small pore diameter.

[0100] Further, in the catalyst-coated filter in which the catalyst layer is formed as described above, even if the fine pores opened at the face into which the aerosol flows of the filter partition wall are the fine pores having a large pore diameter, the pore diameter is not excessively large. Therefore, it is possible to make the inorganic particles locally exist in the vicinity of the face into which the aerosol flows of the filter partition wall.

[0101] As described above, the exhaust gas purifying catalyst of any one of the above-described modes, i.e., the powder-attached catalyst-coated filter is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0102] Figure 1 A cross-sectional view schematically showing the exhaust gas purifying catalyst related to an embodiment of the present application.

[0103] Figure 2 A cross-sectional view showing the porous partition wall of the exhaust gas purifying catalyst shown in Figure 1

[0104] Figure 3 A cross-sectional view further showing the porous partition wall of the exhaust gas purifying catalyst shown in Figure 1

[0105] Figure 4 A cross-sectional view showing a method of separating the fine pores connected in the cross-sectional image of the porous partition wall.

[0106] Figure 5 A plan view schematically showing the surface of the first chamber side of the porous partition wall.

[0107] Figure 6 A composite image in which points having a brightness corresponding to the intensity of the characteristic X-rays from calcium and colored in the image showing the cross section in the thickness direction of the porous partition wall of the exhaust gas purifying catalyst related to Example 1 are overlapped.

[0108] ​​Figure 7 An enlarged view of a cross section of the porous partition of the exhaust gas purification catalyst shown in FIG. 27. Figure 6 An enlarged view of a cross section of the porous partition of the exhaust gas purification catalyst shown in FIG. 27.

[0109] Figure 8 A graph showing the distribution of the powdered inorganic particles in the thickness direction of the porous partition of the exhaust gas purification catalyst relating to Example 1.

[0110] Figure 9 A microscope image of the surface of the first chamber side of the porous partition of the exhaust gas purification catalyst relating to Example 1.

[0111] Figure 10 An image of the points having a brightness corresponding to the intensity of the characteristic X-rays from palladium and colored in FIG. 37. Figure 9 An image of the points having a brightness corresponding to the intensity of the characteristic X-rays from calcium and colored in FIG. 38.

[0112] Figure 11 An image of the points having a brightness corresponding to the intensity of the characteristic X-rays from palladium and colored in FIG. 39. Figure 9 An image of the points having a brightness corresponding to the intensity of the characteristic X-rays from calcium and colored in FIG. 40.

[0113] Figure 12 A composite image obtained by superimposing the image shown in FIG. 41 on the image shown in FIG. 42. Figure 10 A composite image obtained by superimposing the image shown in FIG. 41 on the image shown in FIG. 42. Figure 11 A composite image obtained by superimposing the image shown in FIG. 41 on the image shown in FIG. 42.

[0114] Figure 13 A graph showing the results of line analysis along a straight line on the image shown in FIG. 45. Figure 12 A graph showing the results of line analysis along a straight line on the image shown in FIG. 45. A graph showing the results of line analysis along a straight line on the image shown in FIG. 45.

[0115] A graph showing the results of line analysis along a straight line on the image shown in FIG. 45. Figure 14 Figure 12 A graph showing the results of line analysis along a straight line on the image shown in FIG. 45.

[0116] A graph showing the results of line analysis along a straight line on the image shown in FIG. 45. Figure 15 A graph showing the results of line analysis along a straight line on the image shown in FIG. 45. Figure 12 A graph showing the results of line analysis along a straight line on the image shown in FIG. 45.

[0117] Figure 16 A graph showing the results of measuring the fine pore distribution of the filter partition of the exhaust gas purification catalyst relating to Comparative Examples 1 to 4.

[0118] Figure 17 An image obtained by binarizing the microscope photograph of the porous partition of the exhaust gas purification catalyst relating to Example 1.

[0119] Figure 18 An image obtained by binarizing the microscope photograph of the porous partition of the exhaust gas purification catalyst relating to Comparative Example 3.

[0120] Figure 19A coordinate graph showing the collection efficiency of the exhaust gas purification catalysts relating to Example 1 and Comparative Examples 1 to 4.

[0121] Figure 20 A coordinate graph showing the collection efficiency of the exhaust gas purification catalysts relating to Examples 1 to 3 and Comparative Example 3.

[0122] Figure 21 A coordinate graph showing the initial pressure loss of the exhaust gas purification catalysts relating to Examples 1 to 3 and Comparative Example 3. DETAILED DESCRIPTION

[0123] Hereinafter, with respect to the embodiments of the present application, description will be made with reference to the accompanying drawings. The embodiments described below are embodiments that make any one of the above-described modes more specific.

[0124] Each feature described below can be combined with each of the above-described modes. In addition, a combination of two or more of the features described below can be combined with each of the above-described modes.

[0125] Note that, in the accompanying drawings referred to below, with respect to elements having the same or similar functions, the same reference numerals are attached, and overlapping description is omitted. In addition, in each drawing, the dimensional ratio, shape can be different from the actual one.

[0126] Figure 1 A cross-sectional view of an exhaust gas purification catalyst relating to one embodiment of the present application is shown schematically. Figure 2 A cross-sectional view of the porous partition wall of the exhaust gas purification catalyst shown in Figure 1 is shown in an enlarged manner. Figure 3 A cross-sectional view of the porous partition wall of the exhaust gas purification catalyst shown in Figure 1 is shown in a further enlarged manner. Note that, Figure 1 and Figure 2 In, the hollow arrow indicates the flow direction of exhaust gas.

[0127] Figures 1 to 3 The exhaust gas purification catalyst 1 shown in Figure 2 and Figure 3 is a particulate filter including the catalyst layer 22 shown in. The exhaust gas purification catalyst 1 has a substantially cylindrical shape. As shown in Figure 1 , the exhaust gas purification catalyst 1 has a first end El, a second end E2, a porous partition wall W, a first chamber Cl, and a second chamber C2. The first end El and the second end E2 are the bottom surface of a cylinder.

[0128] The first chamber Cl extends from the first end El toward the second end E2. The first chamber Cl is open at the first end El and is occluded at the second end E2.

[0129] The second chamber C2 extends from the second end E2 toward the first end El. The second chamber C2 is open at the second end E2 and is occluded at the first end El.

[0130] The first chamber Cl and the second chamber C2 are contiguous with a porous partition wall W interposed therebetween. The first chamber Cl and the second chamber C2 are arranged in a pattern in which a checkered pattern (hatched pattern) is formed at the first end El and the second end E2.

[0131] As shown in Figures 1 to 3 , the exhaust gas purification catalyst 1 includes a catalyst-coated filter 2. As shown in Figure 2 and Figure 3 , the catalyst-coated filter 2 includes a filter substrate 21 and a catalyst layer 22.

[0132] As shown in Figure 1 , the filter substrate 21 includes a honeycomb structure 211 and plugs 212a and 212b.

[0133] The honeycomb structure 211 is a cylinder provided with a plurality of through-holes extending from one bottom face to another bottom face. One of the bottom faces corresponds to the first end El, and the other bottom face corresponds to the second end E2. The honeycomb structure 211 includes partition walls 211W constituting side walls of the through-holes. The partition walls 211W are porous and separate adjacent through-holes.

[0134] The plug 212a plugs a portion of the holes of the honeycomb structure 211 on the second end E2 side. The first chamber Cl is located in a space surrounded by the plug 212a that plugs the holes on the second end E2 side and the partition walls 211W constituting the side walls of the holes.

[0135] The plug 212b plugs the remaining holes of the honeycomb structure 211 on the first end El side. The second chamber C2 is located in a space surrounded by the plug 212b that plugs the holes on the first end El side and the partition walls 211W constituting the side walls of the holes.

[0136] The plugs 212a and 212b are arranged so that the holes plugged with the plug 212a on the second end E2 side and the holes plugged with the plug 212b on the first end El side are adjacent with the partition walls 211W interposed therebetween. The first chamber Cl and the second chamber C2 are adjacent with the partition walls 211W of the filter substrate 21 and the catalyst layer 22 provided on the pore walls thereof interposed therebetween.

[0137] As shown in Figure 2 and Figure 3 , the catalyst layer 22 is supported by the filter substrate 21. Specifically, the catalyst layer 22 is provided on the pore walls of the filter substrate 21. That is, the catalyst layer 22 covers the inner pore walls of the partition walls 211W.

[0138] In this structure, the catalyst layer 22 is provided throughout the entire thickness of the porous partition wall W or the partition wall 211W. In the catalyst layer 22, a portion of the inner wall of the fine pores of the partition wall 211W, which is a prescribed value or more from the surface of the first chamber Cl side of the partition wall 211W, can be omitted. That is, the entire catalyst layer 22 can be located in the portion of the porous partition wall W or the partition wall 211W on the first chamber Cl side.

[0139] The partition wall 211W, and the portion of the catalyst layer 22 supported by the partition wall 211W constitute a filter partition wall 21W. The filter partition wall 21W is porous.

[0140] As shown in Figs. 1 and 2, the exhaust gas purifying catalyst 1 further includes inorganic particles 3. The inorganic particles 3 are biased toward the surface on the first chamber Cl side of the porous partition wall W or the filter partition wall 21W or the vicinity thereof. Figure 2 Figure 3 As shown in Figs. 1 and 2, the exhaust gas purifying catalyst 1 further includes inorganic particles 3. The inorganic particles 3 are biased toward the surface on the first chamber Cl side of the porous partition wall W or the filter partition wall 21W or the vicinity thereof.

[0141] The inorganic particles 3 are in a powder form. At least a portion of the inorganic particles 3 is attached to the catalyst-coated filter 2 without being fixed to the catalyst-coated filter 2. In addition, the inorganic particles 3 are not fixed to each other and can be fixed by heat treatment or chemical treatment.

[0142] The inorganic particles 3 reduce the pore diameter of the fine pores located near the surface on the first chamber Cl side of the porous partition wall W. Near the surface on the first chamber Cl side of the porous partition wall W, according to one example, the packing rate of the inorganic particles 3 with respect to the fine pores of the filter partition wall 21W tends to be low in the fine pores having a small opening diameter and tends to be high in the fine pores having a large opening diameter. The packing rate can not follow the above tendency.

[0143] In this exhaust gas purifying catalyst 1, the inorganic particles 3 are biased toward the surface on the first chamber Cl side of the porous partition wall W or the filter partition wall 21W or the vicinity thereof. Therefore, high PM trapping performance can be easily achieved. In addition, in this exhaust gas purifying catalyst 1, the inorganic particles 3 are hardly present in the portion other than the surface on the first chamber Cl side of the porous partition wall W or the filter partition wall 21W or the vicinity thereof. Therefore, the initial pressure loss of this exhaust gas purifying catalyst 1 is small.

[0144] The catalyst layer 22 is preferably configured in such a manner that the filter partition wall 21W has the structure described below.

[0145] ​That is, in terms of the portion of the filter partition wall 21W on the first chamber C1 side, in a cross section of the filter partition wall 21W perpendicular to the surface on the first chamber C1 side, in a case where the pores of the filter substrate 21 are divided into first pores having a pore diameter of 5 μm or more and less than 10 μm, second pores having a pore diameter of 10 μm or more and less than 20 μm, and third pores having a pore diameter of 20 μm or more, the ratio R of the total area S of the portion of the catalyst layer 22 located within the first pores to the total area S of the first pores C1 The total area S of the portion of the catalyst layer 22 located within the second pores to the total area S of the second pores F1 The ratio R of the total area S of the portion of the catalyst layer 22 located within the second pores to the total area S of the second pores F1 The total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores C2 The total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores F2 The ratio R of the total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores F2 The ratio R of the total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores C3 The ratio R of the total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores F3 The ratio R of the total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores F3 The ratio R of the total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores F1 The ratio R of the total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores F2 The ratio R of the total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores F3 The ratio R of the total area S of the portion of the catalyst layer 22 located within the third pores to the total area S of the third pores Figure 4 The boundary between the continuous pores and the pore diameter of each pore are determined using the method described later in

[0146] In such a configuration, for example, the portion of the filter partition wall 21W near the surface on the first chamber C1 side has a narrower pore size distribution and a smaller average pore diameter than the portion of the partition wall 21W near the surface on the first chamber C1 side.

[0147] Figure 4 A cross-sectional view showing a method of separating the continuous pores in the cross-sectional image of the porous partition wall. Figure 4 An image corresponding to the cross section of the porous partition wall W. Note that Figure 4 In the image, the catalyst layer 22 and the inorganic particles 3 described later are omitted.

[0148] (Step S1)

[0149] In this method, first, a cross section of the porous partition wall W is photographed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The cross section is a cross section of the porous partition wall W perpendicular to the surface on the first chamber C1 side, that is, a cross section parallel to the thickness direction of the porous partition wall W.

[0150] (Step S2)

[0151] Next, in the image thus obtained, the partition wall 211W (hereinafter referred to as the partition wall portion) of the filter substrate 21 is identified. Then, within the partition wall portion, the space portion is identified. This includes not only portions separated from the two surfaces of the partition wall 211W, such as space portion CV1, but also portions with openings on at least one surface of the partition wall 211W, such as space portion CV2. A portion of the catalyst layer 22 and the inorganic particles 3 may also be located within the space portion. Then, one of these space portions is selected.

[0152] (Step S3)

[0153] Next, the area of ​​the selected space is calculated, and the diameter of the circle with the same area is calculated, i.e., the equivalent diameter of the circle. Then, it is determined whether the equivalent diameter of the circle is less than 5 μm.

[0154] (Step S4)

[0155] If the equivalent diameter of the circle is 5 μm or less, the previous space portion is determined to be equivalent to a small hole, and the equivalent diameter of the circle is determined as the diameter of the small hole. Then, if there are unselected space portions, one of the unselected space portions is selected, and the process returns to step S3. If there are no unselected space portions, the process ends.

[0156] exist Figure 4 In the example where the spatial portion CV1 is selected, since the equivalent diameter of the circle of the spatial portion CV1 is less than 5 μm, it is determined to be equivalent to a fine hole P1. Then, the equivalent diameter of the circle is determined as the fine hole diameter of the fine hole P1. Then, the unselected spatial portion CV2 is selected, and the process returns to step S3.

[0157] (Step S5)

[0158] When the equivalent diameter of the circle exceeds 5 μm, the aforementioned spatial portion is determined to be equivalent to a spatial portion formed by the connection of two or more fine holes. Then, the spatial portion is divided at a position where the equivalent diameter of the circle is reduced to 50% of the equivalent diameter of the circle, and the boundary between the multiple regions generated therefrom is determined as the boundary of the fine hole.

[0159] exist Figure 4 In the example where spatial section CV2 is selected, since the equivalent diameter of the circle of spatial section CV2 exceeds 5 μm, it is determined to be a spatial section consisting of two or more interconnected micropores. Then, spatial section CV2 is divided at a position where the equivalent diameter of the circle is reduced to 50% of that circle's equivalent diameter, and the boundaries between the resulting multiple regions are defined as the boundaries of the micropores.

[0160] (Sub-step SS1)

[0161] Specifically, first, a plurality of circles that are tangent to both of a pair of wall surface portions that sandwich the space portion and that are opposite each other are generated. Here, the wall surface portions are portions that correspond to boundaries between the space portion and the partition wall portion. Here, only a circle whose center is located between the pair of main surfaces of the partition wall 211W is generated. Then, a reference line is generated by connecting the centers of these circles. In Figure 4 In the example shown, the reference line obtained by connecting the centers of the circles is a broken line CL that branches.

[0162] (Sub-step SS2)

[0163] Next, among the above-mentioned circles, a circle having the largest diameter (hereinafter referred to as a reference circle) is determined. In Figure 4 In the example shown, the circle IC1 is determined.

[0164] (Sub-step SS3)

[0165] Next, for the circles arranged in one direction (hereinafter referred to as a first direction) from the center of the reference circle along the reference line, the diameters are sequentially confirmed from the circle having a short distance from the center of the reference circle. This confirmation is performed until a circle having a diameter of 50% of the diameter of the reference circle is found.

[0166] In a case where such a circle (hereinafter referred to as a first circle) is found, a line segment connecting the first circle and the two cut points of the wall surface portion is determined as a boundary that divides the space portion. In a case where no first circle is found, for the portion of the reference line on the first direction side with respect to the center of the reference circle, no boundary that divides the space portion is determined.

[0167] In Figure 4 In the example shown, for the circles arranged in the downward direction from the center of the circle IC1 along the broken line CL, if the diameters are sequentially confirmed from the circle having a short distance from the center of the circle IC1, the circle IC2 is found as a circle having a diameter of 50% of the diameter of the circle IC1. Therefore, a line segment B1 connecting the circle IC2 and the two cut points of the wall surface portion is determined as a boundary that divides the space portion CV2.

[0168] (Sub-step SS4)

[0169] Next, for the circles arranged in the opposite direction (hereinafter referred to as a second direction) from the center of the reference circle along the reference line, the diameters are sequentially confirmed from the circle having a short distance from the center of the reference circle. This confirmation is performed until a circle having a diameter of 50% of the diameter of the reference circle is found.

[0170] In a case where such a circle (hereinafter referred to as a second circle) is found, a line segment connecting the second circle and the two cut points of the wall surface portion is determined as a boundary that divides the space portion. In a case where no second circle is found, for the portion of the reference line on the second direction side with respect to the center of the reference circle, no boundary that divides the space portion is determined.

[0171] In Figure 4 the example, for the circles arranged in the upward direction from the center of the circle IC1 along the broken line CL, even if the diameters are confirmed in order from the circle whose distance from the center of the circle IC1 is short, no circle whose diameter is 50% of the diameter of the circle IC1 is found. Therefore, for the portion of the broken line CL on the upward direction side with respect to the center of the circle IC1, the boundary of the division space portion CV2 is not confirmed.

[0172] (Sub-step SS5)

[0173] It is judged whether the reference line branches in the range of the portion equivalent to the line connecting the centers of the circles whose diameters are confirmed in the sub-step SS4 or SS5.

[0174] In the case where the reference line branches in the above range, for each branch, the same processing as the sub-step SS4 is performed.

[0175] That is, for the circles arranged in the direction of the branch (hereinafter referred to as the third direction) from the branch point along the reference line, the diameters are confirmed in order from the circle whose distance from the center is short. This confirmation is performed until a circle whose diameter is 50% of the diameter of the reference circle is found.

[0176] In the case where such a circle (hereinafter referred to as a third circle) is found, the line segment connecting the two cut points of the third circle and the wall surface portion is determined as the boundary of the division space portion. In the case where no third circle is found, for the portion of the reference line on the third direction side with respect to the branch point, the boundary of the division space portion is not determined.

[0177] In the case where the above processing is completed or the reference line does not branch in the above range, the next step S6 is entered.

[0178] It is explained that, in Figure 4 the example, the broken line CL does not branch in the range of the portion equivalent to the line connecting the centers of the circles whose diameters are confirmed in the sub-step SS4 or SS5 with the circle IC1 as the reference circle. Therefore, in the case where no additional boundary is determined in the sub-step SS5, the next step S6 is entered.

[0179] (Step S6)

[0180] In the step S6, it is judged whether the boundary is determined in the step S5.

[0181] (Step S7)

[0182] If no boundary is determined in step S5, the previous space is identified as a small hole, and its circular equivalent diameter is determined as the diameter of the small hole. Then, if there are unselected spaces, one of the unselected spaces is selected, and the process returns to step S3. If there are no unselected spaces, the process ends.

[0183] (Step S8)

[0184] If more than one boundary is determined in step S5, in the multiple regions into which the previous space is divided using the boundary, the region where the center of the reference circle is located is determined as a small hole, and its circle equivalent diameter is determined as the small hole diameter.

[0185] Next, the portion of the space excluding the area where the center of the reference circle is located is defined as a new space. Then, this space is selected, and the process returns to step S3.

[0186] exist Figure 4 In the example, in the multiple regions divided by boundary B1 into the spatial portion CV2, the region where the center of circle IC1 is located is identified as a small hole P2, and its circular equivalent diameter is determined as the aperture diameter of small hole P2. Then, the portion of spatial portion CV2 excluding the region corresponding to the small hole P2 where the center of circle IC1 is located (hereinafter referred to as the first residual portion) is identified as a new spatial portion. Then, this spatial portion is selected, and the process returns to step S3.

[0187] Since the equivalent diameter of the first fragment exceeds 5 μm, circle IC3 is determined as the reference circle in step S5. It can be noted that regenerating the reference line is not necessary. In step S5, circles IC4a and IC4b, with diameters 50% of the diameter of circle IC3, are further determined along with boundaries B1 and B2. Next, after step S6, in step S8, the region where the center of circle IC2 is located within the multiple regions divided by boundaries B1 and B2 is identified as a fine hole P3, and its equivalent diameter is determined as the fine hole diameter of fine hole P3. Then, the portion of the first fragment excluding the region corresponding to the fine hole P3 where the center of circle IC2 is located (hereinafter referred to as the second fragment) is determined as a new spatial portion. Then, this spatial portion is selected, and the process returns to step S3.

[0188] Since the equivalent circular diameter of the second fragment is less than 5 μm, in step S4, it is determined that the second fragment corresponds to a fine hole P4, and its equivalent circular diameter is determined as the fine hole diameter of the fine hole P4. Then, if there are unselected spaces, one of the unselected spaces is selected, and the process returns to step S3. If there are no unselected spaces, the process ends.

[0189] The porous partition wall W preferably has the following characteristics.Figure 4 The structure is explained.

[0190] Figure 5 A plan view of the surface of the first chamber side of the porous partition wall is shown in schematic form. Figure 5 The surface of the first chamber C1 side of the porous partition W is depicted.

[0191] In this surface, the pores P of the porous partition wall W are divided into first small pores with an opening diameter of less than 40 μm and first large pores with an opening diameter of more than 40 μm. For example, in Figure 5 In the diagram, the smaller aperture P located at the bottom right and top left is the first large aperture, and the remaining apertures P are the first small apertures. It should be noted that the circle formed by the dashed line LL2 has an area equal to the opening area of ​​aperture P. Therefore, the opening diameter of aperture P is the diameter of the circle formed by the dashed line LL2.

[0192] Furthermore, on the surface of the filter septum 21W, corresponding to the porous septum W in the catalyst-coated filter, the pores of the filter septum 21W are divided into second small pores with an opening diameter of less than 40 μm and second large pores with an opening diameter of more than 40 μm. For example, in Figure 5 In the filter partition 21W, among the fine pores, the pores located in the lower right and upper left are the second largest fine pores, and the remaining pores are the second smallest fine pores. It should be noted that... Figure 5 In the filter partition 21W, the pores are the area enclosed by the solid line LL1. Therefore, the opening diameter of the pores in the filter partition 21W is the diameter of a circle with an area equal to that of the area enclosed by the solid line LL1.

[0193] The total area S of the second micropore S2 The total area S of the first small pore S1 The difference S S2 -S S1 The total area S relative to the second smallest pore S2 The ratio (S) S2 -S S1 ) / S S2 It is below 40%. Additionally, the total area S of the second largest pore... L2 The total area S of the first large fine hole L1 The difference S L2 -S L1 The total area S relative to the second largest fine pore L2 The ratio (S) L2 -S L1 ) / S L2 It is over 60%.

[0194] In this structure, the second large pores have a greater degree of reduction in the opening diameter caused by the application of the inorganic particles 3 than the second small pores. Such a configuration is advantageous, for example, in reducing pores P in which the opening diameter is excessively large or small at the surface of the first chamber side of the porous partition wall.

[0195] Example

[0196] Hereinafter, a specific example of the present application will be described.

[0197] Manufacture of Catalyst for Purification of Exhaust Gas

[0198] Example 1

[0199] A catalyst for purification of exhaust gas was manufactured using the following method. Figure 5 A catalyst for purification of exhaust gas was manufactured using the following method.

[0200] First, 3 parts by mass of a palladium nitrate solution, 35 parts by mass of an alumina powder, 32 parts by mass of an oxide containing cerium dioxide, and ion exchange water were mixed. In this mixture, 1 part by mass of a polycarboxylic acid was mixed to prepare a slurry. The viscosity η of this slurry was 100 mPa-s at a temperature of 25°C and a shear rate of 400 s -1 400

[0201] Next, a filter substrate was prepared. Among them, a filter substrate having a cylindrical shape with a height of 127 mm and a volume of 2.1 L was used.

[0202] Next, the above slurry was supplied to one end surface (first end surface) of the filter substrate, and gas in the filter substrate was sucked from the other end surface (second end surface) of the filter substrate. This suction was performed at a temperature of 25°C under conditions in which the linear velocity (wind speed) of the gas flow near the end portion of the filter substrate when the filter substrate was set and the supply of the slurry was not performed was 50 m / s. In this way, the partition wall of the filter substrate was coated with the slurry. Note that the supply of the slurry was performed in a catalyst-coated filter in such a manner that the amount of the catalyst layer with respect to the volume of the filter substrate was 75 g / L.

[0203] Then, the filter substrate coated with the slurry was dried and fired.

[0204] In this way, a catalyst-coated filter was obtained.

[0205] Next, inorganic particles were supplied to one surface of each filter partition wall of the catalyst-coated filter. Specifically, an aerosol containing inorganic particles as aerosol particles was supplied to a first end portion of the catalyst-coated filter corresponding to the first end surface. At the same time, gas in the catalyst-coated filter was sucked from a second end portion of the catalyst-coated filter corresponding to the second end surface. This suction was performed with the catalyst-coated filter set in such a manner that the first end portion was directed downward.​​

[0206] The volume of inorganic particles relative to the filter substrate was set to 5 g / L. Sepiolite with an average particle size of 6 μm was used as the inorganic particles.

[0207] As described above, a catalyst for purifying waste gas is obtained.

[0208] <2> Determination of Inorganic Particle Distribution

[0209] For the catalyst for exhaust gas purification involved in Example 1, the distribution of inorganic particles in the thickness direction of the porous partition wall was measured. Specifically, for the catalyst for exhaust gas purification involved in Example 1, a cross-section of its porous partition wall was photographed using a scanning electron microscope to obtain a grayscale image. This photographing was performed on a cross-section of the portion of the porous partition wall where the distance to the first end and the distance to the second end are equal. Next, the intensity of characteristic X-rays from calcium was measured by specifying the analysis position obtained using an energy-dispersive X-ray analyzer in the previous grayscale image. Line analysis was performed along the thickness direction of the porous partition wall. Then, a composite image was generated by overlapping the points in the previous grayscale image that had brightness (depth value) corresponding to the intensity of the characteristic X-rays and were colored. From this composite image, the relationship between the distance and depth value to the surface on the first chamber side of the catalyst-coated filter was determined.

[0210] Figures 1 to 3 This is a composite image formed by overlapping colored points with brightness corresponding to the intensity of characteristic X-rays from calcium in an image of a cross-section of the porous partition wall of the exhaust gas purification catalyst shown in Example 1 in the thickness direction. Figure 6 In the middle, the first chamber is located on the upper part of the porous partition wall of the catalyst for exhaust gas purification.

[0211] Figure 6 To be Figure 7 The composite image shows a magnified cross-section along the thickness direction of the porous partition wall of the catalyst used for exhaust gas purification. Figure 6 The white curve in the center represents the boundary between the filter substrate and the first chamber. Figure 7 In the diagram, the white areas represent inorganic particles, the light gray areas represent the catalyst layer, and the dark gray areas represent the filter substrate. For example... Figure 7 As shown, a large number of inorganic particles exist in the fine pores of the filter partition on the first chamber side.

[0212] Figure 7 This is a coordinate graph showing the distribution of powdery inorganic particles along the thickness direction obtained from the porous partition of the catalyst used for exhaust gas purification in Example 1. Figure 8 In the diagram, the horizontal axis represents the distance from the surface of the first chamber side of the catalyst-coated filter, and the vertical axis represents the aforementioned depth values. Figure 8In the present embodiment, a positive value is assigned to the distance of the inorganic particles present inside the filter partition of the catalyst-coated filter. In addition, a negative value is assigned to the distance of the inorganic particles present outside the filter partition of the catalyst-coated filter (i.e., inside the first chamber).

[0213] As shown in Fig. 1, in the catalyst for exhaust gas purification according to Example 1, the inorganic particles are biased toward the first chamber side of the porous partition. In addition, in the catalyst for exhaust gas purification according to Example 1, the above-described amounts A, Al, and A2 satisfy the relationship represented by the inequality (Al + A2) / A > 90%. Figure 8 Specifically, the ratio (Al + A2) / A is 98.7%. Here, Al is the total of each depth value in the range of -50 μm or more and less than 0 μm from the catalyst-coated filter. A2 is the total of each depth value in the range of 0 μm or more and 40 μm or less from the catalyst-coated filter. A is the total of each depth value in the range of -50 μm or more and 200 μm or less from the catalyst-coated filter.

[0214] In addition, in the catalyst for exhaust gas purification according to Example 1, the amount of the inorganic particles present inside the fine pores of the filter partition is 70% or more of the total amount of the inorganic particles. Specifically, the amount of the inorganic particles present inside the fine pores of the filter partition is 77.4% of the total amount of the inorganic particles. Here, the amount of the inorganic particles present inside the fine pores of the filter partition is the total of each depth value in the range of 0 μm or more and 200 μm or less from the catalyst-coated filter. In addition, the total amount of the inorganic particles is the total of each depth value in the range of -50 μm or more and 200 μm or less from the catalyst-coated filter.

[0215] (3) Measurement of Catalyst Layer Distribution and Inorganic Particle Distribution

[0216] The catalyst layer distribution and the inorganic particle distribution were measured for the catalyst for exhaust gas purification according to Example 1. Specifically, first, for the catalyst for exhaust gas purification according to Example 1, a surface of the first chamber side of the porous partition was photographed using a scanning electron microscope, to obtain a microscope photograph. This photographing was performed with respect to a cross section of the porous partition at a position equidistant from the first end and the second end. Next, in the previous microscope photograph, analysis positions obtained using an energy dispersive X-ray analysis device were specified, and an image showing points colored with brightness corresponding to the intensity of characteristic X-rays from palladium was obtained. Next, in the previous microscope photograph, analysis positions obtained using an energy dispersive X-ray analysis device were specified, and an image showing points colored with brightness corresponding to the intensity of characteristic X-rays from calcium was obtained.

[0217] Figure 8A microscope photograph showing the surface of the first chamber side of the porous partition of the exhaust gas purification catalyst involved in Example 1. Figure 9 A microscope photograph showing the surface of the first chamber side of the porous partition of the exhaust gas purification catalyst involved in Example 1. Figure 10 An image in which points having a brightness corresponding to the intensity of characteristic X-rays from palladium and being colored are present. Figure 9 An image in which points having a brightness corresponding to the intensity of characteristic X-rays from palladium and being colored are present. Figure 10 The position of the catalyst layer. Figure 9 An image in which points having a brightness corresponding to the intensity of characteristic X-rays from calcium and being colored are present. Figure 11 An image in which points having a brightness corresponding to the intensity of characteristic X-rays from calcium and being colored are present. Figure 9 An image in which points having a brightness corresponding to the intensity of characteristic X-rays from calcium and being colored are present. Figure 11 The position of the inorganic particles.

[0218] Figure 9 Points having a brightness corresponding to the intensity of characteristic X-rays from palladium and being colored present in a portion close to the surface of the porous partition of the exhaust gas purification catalyst. In addition, Figure 10 Points having a brightness corresponding to the intensity of characteristic X-rays from calcium and being colored present in a portion close to the surface of the porous partition of the exhaust gas purification catalyst.

[0219] Figure 11 A composite image in which the image shown in Figure 12 is overlaid with the image shown in Figure 10 .

[0220] Figure 11 Each of the graphs shown in Figures 13 to 15 is a graph showing the results of line analysis along a certain straight line on the image shown in Figure 12 . With line analysis, the depth values of points having a brightness corresponding to the intensity of characteristic X-rays from palladium and being colored and the depth values of points having a brightness corresponding to the intensity of characteristic X-rays from calcium and being colored are analyzed in a certain straight line on the image shown in Figure 12 The results of line analysis along a straight line present at a position 60 pixels from the left end in the case where the length in the lateral direction of the image shown in Figure 13 is set to 250 pixels and the length in the vertical direction is set to 200 pixels. Figure 12 The results of line analysis along a straight line present at a position 120 pixels from the left end in the case described above. In the case described above, Figure 14 line analysis is performed along a straight line present at a position 180 pixels from the left end. The depth values are obtained using ImageJ. In the line analysis described above, the position of the upper end of the image shown in Figure 15 is set to 0 pixels and the position of the lower end is set to 200 pixels.

[0221] As described above, Figure 12This shows colored points with brightness corresponding to the intensity of characteristic X-rays from palladium, located relatively close to the surface of the porous partition wall of the catalyst used for exhaust gas purification. Additionally, Figure 10 This shows colored points with brightness corresponding to the intensity of characteristic X-rays from calcium, present in the portion near the surface of the porous partition wall of the catalyst for exhaust gas purification; these are inorganic particles present in the portion near the surface of the porous partition wall. For example... Figure 11 As shown, the intensity values ​​of palladium and calcium are inversely correlated. The smaller palladium intensity values ​​indicate finer pores. This suggests that inorganic particles are located within the fine pores of the filter septum. Furthermore, areas with higher palladium concentrations have smaller pore sizes, while areas with lower palladium concentrations or no palladium detected have larger pore sizes. Additionally, in… Figures 13 to 15 In the sample, compared to the regions with higher palladium content, a large amount of calcium is present in the regions with lower palladium content. This indicates that... Figures 13 to 15 In contrast to pores with relatively small pore diameters, pores with relatively large pore diameters contain a large number of inorganic particles.

[0222] (Example 2)

[0223] The ratio of the amount of inorganic particles to the volume of the filter substrate was changed from 5 g / L to 1 g / L. Otherwise, the same method as in Example 1 was used to manufacture the catalyst for exhaust gas purification.

[0224] (Example 3)

[0225] The ratio of the amount of inorganic particles to the volume of the filter substrate was changed from 5 g / L to 20 g / L. Otherwise, the same method as in Example 1 was used to manufacture the catalyst for exhaust gas purification.

[0226] (Comparative Example 1)

[0227] Prepare the filter substrate used in Example 1, and use it as a catalyst for exhaust gas purification in Comparative Example 1.

[0228] (Comparative Example 2)

[0229] The ratio of the amount of catalyst layer to the volume of the filter substrate was changed from 75 g / L to 50 g / L, and the supply of inorganic particles to the catalyst-coated filter was omitted. Otherwise, the same method as in Example 1 was used to manufacture the catalyst for exhaust gas purification.

[0230] (Comparative Example 3)

[0231] The supply of inorganic particles to the catalyst-coated filter is omitted, and the catalyst for exhaust gas purification is manufactured using the same method as in Example 1. That is, the catalyst-coated filter is manufactured using the same method as in Example 1 and is used as the catalyst for exhaust gas purification in Comparative Example 3.

[0232] (Comparative Example 4)

[0233] The ratio of the amount of catalyst layer to the volume of the filter substrate was changed from 75 g / L to 100 g / L, and the supply of inorganic particles to the catalyst-coated filter was omitted. Otherwise, the same method as in Example 1 was used to obtain the catalyst for exhaust gas purification.

[0234] <4> Determination of D1 / D2

[0235] For the catalysts used in exhaust gas purification in Comparative Examples 1 to 4, the pore distribution of the filter septum was determined using the mercury infiltration method. The results are shown below. Figures 13 to 15 . Figure 16 The vertical axis represents the logarithmic differential pore volume (mg / L). Figure 16 The horizontal axis represents the fine aperture. According to... Figure 16 The average pore sizes of the filter partitions of the catalysts used for exhaust gas purification in Comparative Examples 1 to 4 are 17.0 μm, 10.5 μm, 10.0 μm, and 8.5 μm, respectively. Therefore, the ratio D1 / D2 of the average particle size D1 of the inorganic particles in the catalysts used for exhaust gas purification in Examples 1 to 3 to the average pore size D2 of the filter partitions is 0.6.

[0236] <5> Determination of aperture

[0237] For each of the catalysts for exhaust gas purification involved in Examples 1 to 3 and Comparative Examples 2 to 4, the opening diameter at the surface of the first chamber side of the porous partition was measured using the method described above. The results are shown in Table 1.

[0238] [Table 1]

[0239]

[0240] Figure 16 This is an image generated by binarizing a microscope image of the porous partition of the catalyst used for exhaust gas purification in Example 1. Figure 17 This is an image obtained by binarizing a microscope image of the porous partition of the catalyst used for exhaust gas purification in Comparative Example 3.

[0241] In Table 1, “S ＜20 / S” represents the total area S of pores with an opening diameter of less than 20 μm in a microscopic photograph of the surface of the first chamber side of the porous partition. ＜20 The proportion of the total area S of all the fine pores. 20-40S" is the total area S of the fine pores having an opening diameter in the range of 20 μm or more and less than 40 μm in the above-mentioned photomicrograph 20-40 The proportion in the total area S of all the fine pores. "S 40-60 S" is the total area S of the fine pores having an opening diameter in the range of 40 μm or more and less than 60 μm in the above-mentioned photomicrograph 40-60 The proportion in the total area S of all the fine pores. "S 60-80 S" is the total area S of the fine pores having an opening diameter in the range of 60 μm or more and less than 80 μm in the above-mentioned photomicrograph 60-80 The proportion in the total area S of all the fine pores. "S 80-100 S" is the total area S of the fine pores having an opening diameter in the range of 80 μm or more and less than 100 μm in the above-mentioned photomicrograph 80-100 The proportion in the total area S of all the fine pores. "S 100＜ S" is the total area S of the fine pores having an opening diameter of 100 μm or more in the above-mentioned photomicrograph 100＜ The proportion in the total area S of all the fine pores. "S S S" is the total area S of the fine pores having an opening diameter of less than 40 μm in the above-mentioned photomicrograph S The proportion in the total area S of all the fine pores.

[0242] As Figure 18 and Figure 17 and Table 1, in the exhaust gas purification catalysts relating to Examples 1 and 3, the proportion of the fine pores having a large opening diameter on the surface of the first chamber side of the porous partition wall was small as compared with the exhaust gas purification catalysts relating to Comparative Examples 2 to 4.

[0243] <6> Measurement of Filling Rate

[0244] For the exhaust gas purification catalyst relating to Example 1, the above-mentioned ratios (S S2 -S S1 ) / S S2 and the ratio (S L2 -S L1 ) / S L2 .

[0245] Specifically, for the exhaust gas purification catalyst relating to Example 1, the total area S ＜20 and S 20-40 obtained at the time of the calculation of the opening diameter described above were added to give the total area S S1 of the exhaust gas purification catalyst relating to Example 1. In addition, for the exhaust gas purification catalyst relating to Example 1, the total areas S 40-60 , S 60-80 , S80-100 and S 100＜ the sum of S L1 . In addition, for the exhaust gas purification catalyst relating to Comparative Example 3, the sum S ＜20 and S 20-40 the sum of S S2 . In addition, for the exhaust gas purification catalyst relating to Comparative Example 3, the sum S 40-60 , S 60-80 , S 80-100 and S 100＜ the sum of S L2 . For the exhaust gas purification catalysts relating to Examples 2 and 3, the same method as that of Example 1 was employed to obtain the ratio (S S2 -S S1 ) / S S2 and the ratio (S L2 -S L1 ) / S L2 . The results of the calculation are shown in Table 2 below.

[0246] [Table 2]

[0247]

[0248] As shown in Table 2, in the exhaust gas purification catalyst relating to Example 1, the ratio (S L2 -S L1 ) / S L2 was larger than the ratio (S S2 -S S1 ) / S S2 . That is, in the exhaust gas purification catalyst relating to Example 1, among the pores opening on the surface of the first chamber side of the porous partition wall, the pores having a large opening diameter had a higher packing rate of the inorganic particles than the pores having a small opening diameter.

[0249] <7> Measurement of the collection efficiency with respect to the number (PN) of PM

[0250] For the exhaust gas purification catalyst relating to Example 1, the collection efficiency of PM was obtained by the following method. Specifically, light oil was burned by a soot generator to generate PM, and the exhaust gas purification catalyst relating to Example 1 was allowed to accumulate the PM. At the time when the amount of accumulation of PM reached 0.02 g / L, the number of PM discharged from the exhaust gas purification catalyst was measured. The measurement of the number of PM was performed by setting the gas temperature to 240°C and the gas flow rate to 250 kg / hour.

[0251] Next, the number of PM was measured upstream of the exhaust gas purifying catalyst relating to Example 1 in a soot generator. For the measurement of the number of PM, the gas temperature was set to 240°C and the gas flow rate was set to 250 kg / hour.

[0252] Next, for the exhaust gas purifying catalyst relating to Example 1, the collection rate was calculated according to the following formula (1).

[0253] [Table 1]

[0254]

[0255] In the above formula (1), xl is the number of PM discharged from the exhaust gas purifying catalyst relating to Example 1, and xo is the number of PM upstream of the exhaust gas purifying catalyst relating to Example 1.

[0256] Next, for the exhaust gas purifying catalysts relating to Examples 2 and 3 and Comparative Examples 1 to 4, the collection rate was obtained by the same method as explained for Example 1.

[0257] The results of the collection rate are shown in Figure 18 and Figure 19 .

[0258] As shown in Figure 20 and Figure 19 , the exhaust gas purifying catalysts relating to Examples 1 to 3 all had excellent PM collection performance.

[0259] <8> Evaluation of Initial Pressure Loss

[0260] For the exhaust gas purifying catalyst relating to Example 1, the initial pressure loss was calculated. Specifically, the pressure loss at a wind speed of 10 m 3 / minute was calculated.

[0261] Next, for the exhaust gas purifying catalysts relating to Examples 2, 3 and Comparative Example 3, the initial pressure loss was investigated by the same method as explained for Example 1.

[0262] The results of the initial pressure loss are shown in Figure 20 .

[0263] As shown in Figure 21 , the exhaust gas purifying catalysts relating to Examples 1 to 3 all had small pressure losses. In particular, the exhaust gas purifying catalysts relating to Examples 1 and 2 had small pressure losses.

[0264] <9> Evaluation of Pressure Loss Due to PM Accumulation

[0265] For each of the exhaust gas purification catalyst bodies relating to Example 1 and Comparative Examples 2 to 4, evaluation of pressure loss was performed. Specifically, light oil was combusted using a soot generator to generate PM, and the PM was accumulated in each of the exhaust gas purification catalyst bodies. At the time when the amount of PM accumulation reached 1 g / L, each of the exhaust gas purification catalysts was subjected to measurement of pressure loss. The measurement was performed with the gas temperature set to 240°C and the gas flow rate set to 250 kg / hour. The results are shown in Table 3.

[0266] [Table 3]

[0267] Table 3

[0268] Figure 21 Pressure loss (mbar) due to PM accumulation 42.6 Example 3 54.1 Comparative Example 2 56.5 Comparative Example 3 65.3

[0269] As shown in Table 3, the exhaust gas purification catalyst relating to Example 1 had a smaller pressure loss after PM accumulation than the exhaust gas purification catalysts relating to Comparative Examples 2 to 4.

[0270] Measurement of packing rate

[0271] For the exhaust gas purification catalysts relating to Examples 1 to 3 and Comparative Examples 2 to 4, the packing rates R F1 , R F2 , and R F3 were calculated using the method described in the Comparative Example 4 Figure 4 Explanation F1 , R F2 , and R F3 . As a result, for the exhaust gas purification catalysts relating to Examples 1 to 3 and Comparative Examples 2 to 4, the packing rates R F1 , R F2 , and R F3 all satisfied the inequalities: R F1 < R F2 < R F3 The packing rate R F1 was in the range of 10 to 40%, the packing rate R F2 was in the range of 15 to 40%, and the packing rate R F3 was in the range of 20 to 45%.

[0272] Explanation of reference signs

[0273] 1...exhaust gas purification catalyst, 2...catalyst-coated filter, 3...inorganic particle, 21...filter substrate, 21W...filter partition wall, 22...catalyst layer, 211...honeycomb structure, 211W...partition wall, 212a...plug, 212b...plug, B1...boundary, B2...boundary, IC1...circle, IC2...circle, IC3...circle, IC4a...circle, IC4b...circle, C1...first chamber, C2...second chamber, CL...dotted line, CV1...space portion, CV2...space portion, E1...first end, E2...second end, P1...pore, P2...pore, P3...pore, P4...pore, W...porous partition wall.

Claims

1. Catalysts for waste gas purification, including: A catalyst-coated filter comprises a filter substrate and a catalyst layer disposed on the pore walls of the filter substrate. It has a first end, a second end, a filter partition, an inlet chamber, and an outlet chamber. The filter partition is porous. The inlet chamber extends from the first end toward the second end, opening at the first end and closing at the second end. The outlet chamber extends from the second end toward the first end, opening at the second end and closing at the first end. The inlet chamber and the outlet chamber are adjacent to each other, with the filter partition sandwiched between them. The powdered inorganic particles, in a cross-section parallel to the thickness direction of the filter partition, are biased towards the surface of the filter partition adjacent to the inlet chamber. The total amount A of the inorganic particles, the amount A1 of the inorganic particles located on the surface of the catalyst-coated filter adjacent to the inlet chamber, and the amount A2 of the inorganic particles within the pores of the catalyst-coated filter, at a distance of less than 20% of the thickness of the portion of the catalyst-coated filter corresponding to the filter partition wall, satisfy the relationship expressed by the inequality (A1+A2) / A≥90%. In the portion of the catalyst for exhaust gas purification corresponding to the filter partition, i.e., the surface of the porous partition on the inlet chamber side, where the pores of the porous partition are divided into first small pores with an opening diameter of less than 40 μm and first large pores with an opening diameter of 40 μm or more, and where the surface of the filter partition on the inlet chamber side is divided into second small pores with an opening diameter of less than 40 μm and second large pores with an opening diameter of 40 μm or more, the total area S of the second small pores is... S2 The total area S of the first small pore S1 The difference S S2 -S S1 The total area S of the second micropore S2 The ratio (S) S2 -S S1 ) / S S2 The total area S of the second largest fine pore is below 40%. L2 The total area S of the first large fine hole L1 The difference S L2 -S L1 The total area S of the second large fine hole L2 The ratio (S) L2 -S L1 ) / S L2 It is over 60%.

2. The catalyst for purifying waste gas according to claim 1, wherein, Most of the inorganic particles are located within the pores of the filter partition.

3. The catalyst for purifying waste gas according to claim 1, wherein, The inorganic particles have an average particle size in the range of 1 to 50 μm.

4. The catalyst for purifying waste gas according to claim 1, wherein, The inorganic particles comprise one or more selected from metal oxides, metal hydroxides, metal carbonates, metal phosphates, metal nitrates, metal sulfates, and clay minerals.

5. The catalyst for purifying waste gas according to claim 1, wherein, The ratio D1 / D2 of the average particle size D1 of the inorganic particles to the average pore size D2 of the filter partition is in the range of 0.15 to 2.

6. The catalyst for purifying waste gas according to claim 1, wherein, The ratio of the mass of the inorganic particles to the volume of the filter substrate is in the range of 3 to 50 g / L.

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